Steel joists have been used to structurally support building roofs and floors throughout the United States for the better part of a century. An exemplary array of conventional joists forming a support for a deck or roof is depicted in FIG. 1. The term “joist”, as used herein, indicates a closely spaced, repetitive member that directly supports (and in combination directly supports) a relatively flat structural element such as a roof deck or floor slab or the like. A steel joist, as opposed to a common truss, is defined by the U.S. Department of Labor in OSHA 29 C.F.R. §1926.751, incorporated fully herein by reference. Joists of identical properties are commonly found in a building in relatively large numbers, and as a result, such joists are currently manufactured in mass quantities. In contrast to the joist, a “girder” is a relatively heavier member that are fewer in number and that directly supports the joists.
The conventional steel joist used today consists of a top chord, a bottom chord, and multiple diagonals. As FIG. 2 indicates, the top chord is a horizontal (or slightly sloped) member that in typical conditions fastens directly to the corrugated metal roof or floor deck that is being supported. The bottom chord is a horizontal member that is beneath and parallel (or nearly parallel) to the top chord. The diagonals (also known as web members) are inclined members arranged in a zig-zag pattern to join the top chord to the bottom chord. All of these members lie in, or nearly in, a common vertical plane.
The top chord of today's conventional steel joist consists of a pair of steel angles, parallel to one another, and positioned in a “back-to-back” orientation. See FIG. 3. The bottom chord also uses this same configuration. The web members are typically fabricated from steel angles or steel rods and are frequently welded in the gap between the parallel steel angles of the top (and bottom) chord.
Well known problems associated with present conventional steel joist constructions include: 1.) the need for erection bracing, also known as erection bridging as defined by OSHA; 2.) poor aesthetics; 3.) potential for corrosion of untreated areas; 4.) proclivity to top and/or bottom chord local bending; 5.) poor power actuated fastener penetration due to top chord local bending; 6.) inability to properly support/distribute and/or aesthetically conceal electrical and plumbing lines and HVAC ductwork. A need, therefore, exists for a steel joist assembly which resolves or greatly reduces these known problems.